Ventilatory efficiency as a sex-dependent determinant of cardiorespiratory fitness in endurance athletes: a cross-sectional study

The relevance of ventilatory efficiency to aerobic performance in endurance athletes remains incompletely understood, particularly when potential sex-related differences are considered. This study investigated whether ventilatory efficiency is associated with cardiorespiratory fitness and whether sex moderates this association in amateur triathletes. In this cross-sectional study, 59 amateur triathletes (37 male and 22 female) performed a maximal cardiopulmonary exercise test on a cycle ergometer. Ventilatory efficiency was assessed using the nadir of the minute ventilation to carbon dioxide production ratio (V̇E/V̇CO 2 ), defined as the lowest continuous 20-second average achieved during test. Cardiorespiratory fitness was assessed by maximal oxygen uptake (V̇O 2 max). Multiple linear regression was used to examine the association between V̇E/V̇CO 2 -Nadir and V̇O 2 max, including an interaction term for sex, followed by sex-stratified analyses. In the overall sample, V̇E/V̇CO 2 -Nadir was significantly associated with lower V̇O 2 max (β = −1.70, p = 0.002). A significant interaction between V̇E/V̇CO 2 -Nadir and sex was also observed (β = 2.19, p = 0.005), whereas the main effect of sex was not significant (β = 0.373, p = 0.877). In female athletes, higher V̇E/V̇CO₂ nadir was associated with lower V̇O₂max (β = −1.64, p = 0.048, R² = 0.223), whereas no significant association was observed in male athletes (β = 0.49, p = 0.343, R² = 0.026). Overall, these findings suggest that the association between ventilatory efficiency and cardiorespiratory fitness may differ according to sex. While V̇E/V̇CO₂ nadir was associated with V̇O₂max in female athletes, this relationship was not observed in males, indicating a potential sex-dependent interaction that warrants confirmation in larger studies.